Current-limiting electric switch

ABSTRACT

A current-limiting electric switch is disclosed, of the kind having at least one release per pole, each release comprising two contacts carried by respective supporting members, said contacts being electrically connected to a feed and a load terminal through a current path of which said supporting members form, when the contacts are closed, two parallel branches through which currents of opposite sign flow, so that a current increase beyond a preselected limit produces in said two branches electrodynamic repulsion forces to overcome the bias of resilient supporting members and to cause the supporting members to be set apart for separating the contacts, the improvement consisting in the fact that said parallel branches are a part of a closed loop which is made up by said current path in correspondence with each release. The switch according to this invention permits to construct apparatus having shorter working times than those of the prior art and a more reliable operability.

United States Patent [191 Mostosi Oct. 9, 1973 CURRENT-LIMITING ELECTRICSWITCH [75] Inventor: Angelo Mostosi, Bergamo, Italy [73] Assignee:S.A.C.E. S.p.A. Construzioni Elettromeccaniche, Bergamo, Italy 22 Filed:Feb. 2, 1972 21 Appl. No.: 222,953

[30] Foreign Application Priority Data Primary Examiperl-larold Broome[57] ABSTRACT A current-limiting electric switch is disclosed, of thekind having at least one release per pole, each release comprising twocontacts carried by respective supporting members, said contacts beingelectrically connected to a feed and a load terminal through a currentpath of which said supporting members form, when the contacts areclosed, two parallel branches through which currents of opposite signflow, so that a current increase beyond a preselected limit produces insaid two branches electrodynamic repulsion forces to overcome the biasof resilient supporting members and to cause the supporting members tobe set apart for separating the contacts, the improvement consisting inthe fact that said parallel branches are a part of -a closed loop whichis made up by said current path in correspondence with each release. Theswitch according to s more reliable operability.

9 Claims. 17 Drawing Figures PATENTED 75 SHEET 10F 8 PATENTEDBBI 919133.764. 946

SHEET 2 0F 8 PATENTEUUBI ems SHEET 8 IF 8 CURRENT-LIMITING ELECTRICSWITCH This invention relates to a current-limiting electric switch,which is particularly adapted to apparatus intended to operate in thefield of low voltages (up to 1,000 volts) and with currents in the orderof magnitude of a few hundreds of amperes on continuous duty, whereinthe switch release under overcurrent conditions due to short circuitingis automatically brought about by the electrodynamic repulsion forces asproduced by the flow of strong currents of opposite signs through twoparallel and properly approached branches of the current path whichconnects the movable and the fixed contacts of the switch to the feedingand loading terminals, said parallel branches being usually thesupporting members themselves for the movable and the fixed contacts,

There are known at present two kinds of currentlimiting switcheswhose'release is caused by the electrodynamic forces as produced by thecurrent flowing through said switches, that is, switches having one ormore releases per each pole and in which the fixed and the movablecontacts are connected to the feeding and loading terminals through acurrent path forming an open loop, of which the supporting members ofthe contacts form two parallel branches through which currents ofopposite signs flow, and switches having two releases per pole in whichthe fixed and the movable contacts are connected to the feeding andloading terminals through a currentpath forming a single closed loop, ofwhich the supporting members for the contacts form two parallel branchesthrough which currents of opposite sign flow.

An object of the present invention is to provide a current-limitingelectric switch having a higher interrupting capacity. that is, acurrent-limiting electric switch wherein the electric connection betweenthe fixed and movable contacts and the feed and load terminals isobtained in such a way as to produce higher repulsion forces and thus ahigher contact-separation speed, the impressed currents being equal, orequal repulsion forces when the impressed current is lower.

The object of the invention is achieved by means of a current-limitingelectric switch equipped with at least a release per pole, each releasecomprising two contacts carried by the respective supporting members,said contacts being electrically connected to a feed and a load terminalthrough a current path of which, when the contacts are closed, saidsurpports form two parallel branches through which currents of oppositesigns flow, so that a current increase above a predetermined limitproduces in said branches electrodynamic repulsion forces capable ofovercoming the bias of resilient retaining members and of causing thesupporting members to be driven apart from one another for theseparation of the contacts, characterized in that said parallel branchesare a part ofa closed loop as formed by said current path incorrespondence with each interruption.

It is apparent that this arrangement introduces a substantialimprovements over the conventional art both in the case of a switchhaving a single interruption per hole (current path with a single closedloop) and in the case of a switch having two interruptions per pole(current path with two closed loops), inasmuch that every couple ofcontacts, that is, each release, is associated with a respective closedloop of current, that which permits to obtain higher repulsion forcesand thus high contact-separation speeds when the impressed currents areequal, or equal repulsion forces with lower currents, that is, withsmaller current values which originate the contact separation.

Summing up, the switch according to the present invention permits toconstruct apparatus which are characterized, as compared with theconventional constructions, by shorter operation times and thus, thearcextin-guishing means being the same, by a higher ability to limit themaximum value of the current and energy that the switch allows to beestablished under shortcircuit conditions.

The features of the present invention, along with the advantagesderiving therefrom, will be better understood upon a scrutiny of theensuing detailed description ofa few possible embodiments thereof. Insuch detailed description, which is given by way of a nonlimitingexample only, reference will be had to the accompanying drawings,wherein FIGS. 1, 2, 3 and 4 are vertical cross-sectional views showing,in four different working conditions, a pole of a two-release switchaccording to a preferred embodiment of the invention.

FIG. 5 is a partial cross-sectional view taken along the line VV of FIG.1.

FIGS. 6, 7 and 8 are diagrammatical elevational views showing threedifferent operative conditions of a pole of a switch having two releasesper pole according to another possible embodiments of the invention.

FIGS. 9, 10 and 11 are diagrammatical elevational views showing threedifferent working conditions of a pole ofa switch having two releasesper pole according to still another embodiment of the invention.

FIGS. 12, 13 and 14 are diagrammatical elevational views showing threedifferent working conditions of a pole of a switch having two releasesper pole according to a further possible embodiment of the invention.

FIGS. l5, l6 and 17 are diagrammatical elevational views showing threedifferent working conditions of a pole of a switch having a singlerelease per pole according to still another embodiment of the invention.

The switch shown in FIGS. l-S, comprises, above all, a fixed frame 1, ofan electrically insulating material, which supports two stiff conductors2-3 which can be connected to electric feed and load cables (not shown)by means of terminal clamps 4-5 equipped with set screws 6-7 and anannular conducting plate 8 which is the supporting member for two fixedcontacts 9-10. In the interior of the hole of the conducting plate 8there is, slidably housed, a shaped rod 11, of an electricallyinsulating material, which is driven so as to be shifted between theposition of FIG. 1 and the position of FIG; 4, by the agency of a lever12 keyed to an actuating shaft 13. To the rod 11 are pivoted at 14-15two movable arms 16-17 of an electrically conducting material, which areelectrically connected to the rigid conductors 2-3 by means of flexiblecables 18-19 and carry the respective movable contacts 20-21 cooperatingwith the fixed contacts 9-10. The two movable arms 16-17, furthermore,carry the respective pins 22-23 which engage the corresponding ends oftwo compression springs 24-25, whose other ends engage, at 26-27, theslidable rod 11. Lastly, the two movable arms 16-17 carry the respectivecouples of trunnions 28-29 (FIG. 5) whose function will become clearerhereinafter. To the fixed frame 1 is then coupled a lid 30, also of anelectrically insulating material,.which, along with the framingaforementioned, defines two areextinguishing chambers 31-32, withinwhich respective arc-splitting sets of ferromagnetic plates 33-34, arehoused.

Assuming that the terminal 4 is connected to a feeding source and theterminal 5 is connected to a load, the result is that, until such timeas the movable contacts -21 are in their closed position where theycontact the fixed contacts 9-10 (FIG. 1), an electric circuit, having adouble closed loop going from the terminal 4 to the terminal 5 throughthe rigid conductor 2, the flexible cable 18, the movable arm 16, themovable contact'20, the fixed contact 9, the conducting plate 8, thefixed contact 10, the movable contact 21, the movable arm 17, theflexible cable 19 and the rigid conductor 3, is made. Under theseconditions, the springs 24-25 act on the movable arms 16-17 so as tocause them to rotate in the clockwise and anticlockwise direction,respectively, thus maintaining a close contact between the movablecontacts 20-21 and the fixed contacts 9-10.

Whenever a short-circuit or anyhow a strong overcurrent condition isexperienced, the strong currents of opposite signs which flow throughthe movable arm 16 and the fixed plate 8 (parallel branches of the firstclosed loop) and those, also of opposite signs which flow through thefixed plate 8 and the movable arm 17 (parallel branches of the secondclosed loop), produce intense electrodynamic repulsive forces, whichurge the movable arms 16-17 to be rotated in the anticlockwise directionand the clockwise direction, respectively, so as to give rise to theseparation of the movable contacts 20-21 from the fixed contacts 9-10(the arcs which are thus formed are simultaneously urged by theelectrodynamic forces which always try to widen a current loop and aredrawn into the interior of the arc chamber by the ferromagnetic materialplates 33-34)? During the first portion of their contact-separationmovement, the movable arms 16-17 are biassed by the bias of the springs24-25; then, as the axes of the spring have attained and overtaken theline jointing the pins 26-14 and 27-15, the couple of springs isinverted and the movable-arms 16-17 are quickly driven towards theposition of maximum rotation which is-defined by the abutment betweenthe back of the arms and a central core 35 of the shaped rod 11 (FIG.2). Subsequently, the action of an appropriate element which issensitive to strong current intensities (not shown in the drawings) ashoused in the container 41, causes a clockwise rotation of the drivingshaft 13 (as an alternative, if the sensitive member aforesaid is notmounted in the switch, said clockwise rotation of the shaft 13 can bemanually obtained by the agency of the lever 38). This fact causes theshift (towards the left with respect to FIG. 2) of the shaped rod 11 andthe resultant similar displacement of the movable arms 16-17, whichmeet, at a certain spot, specially provided ribs 36-37 of the lid 30(FIG. 3), which cause the rotation thereof (clockwise and anticlockwise,respectively) until the jointing lines of the pins 26-14 and 27-15 areovercome in the reverse direction by the axes of the springs 24-25 andthe trunnions 28-29 of the movable arms 16-17 go to rest againstspecially provided bracket-like projections 39-40 of the shaped rod 11.As the switch reaches the end position of FIG. 4, as defined byappropriate end-of-stroke abutments coupled to the shaft 13 (and notshown in the drawings), the switch is in readiness for a newcircuit-closing operation, which can be easily performed by acting uponthe driving member 38 so as to rotate the shaft 13 in the reversedirection.

Of course, in the practical embodiment of the switch according to FIGS.1-5, means should also be provided which are capable of allowing themanual release by an operator, as well as the release in the case ofovercurrents which are not strong enough to originate suchelectrodynamic forces as to overcome the bias of the springs 24-25.These means, at any rate, are not a part of the claimed invention andare thus not described herein in detail, or shown in the drawings,either. They are intended, in any case, to act upon the driving shaft 13so as to cause the rotation from the position of FIG. 1 to the positionof FIG. 4, so as to cause the shift of the rod 11 and of the arms 16-17from the closed position of FIG. 1 to the opened position of FIG. 4,said shift being an integral movement on account of the abutment betweenthe trunnions 28-29 of the arms 16-17 and the bracket-like projections39-40 of the rod 11.

The basic features of the present invention are maintained unalteredalso in the embodiment shown in FIGS. 6 to 8, which diagrammaticallyshow a pole of aswitch having two releases per pole, in which the twocouples of fixed and movable contacts of the two releases are connectedto the feeding and loading terminals (not shown) by a currentpath havingtwo closed loops (as indicated by the arrows A) which comprises a firstrigid conductor 51, a first flexible cable 53, a first movable arm 55, afirst movable contact 57, a first fixed contact 59, a conducting plate61, a second fixed contact 60, a second movable contact 58, a secondmovable arm 56, a second flexible cable 54 and a second rigid conductor52. The two movable arms 55-56 are pivoted to respective fixed pivotpins 62-63 and are driven towards the closed position of FIG. 6 bysprings 64-65 arranged between pins 66-67 as carried by the movable arms55-56 and pins 68-69 as carried by movable supporting members 70-71 alsopivotedto the fixed pins 62-63 and linkably connected by tie rods 72-73to a slidable rod 74 driven by a lever 75 keyed to a driving shaft 76,which is controlled in the same way as the shaft 13 of the embodiment ofthe FIGS. 1 to 5. 1

In operation, whenever a short-circuit or anyhow a strong overcurrent isexperienced, the high electrodynamic forces as produced by the currentsof opposite signs which flow through the movable arm 55 and the plate 61(first closed loop) and the plate 61 and the movable arm 56 (secondclosed loop) urge the movable arms 55-56 to overcome the bias of thesprings 64-65 (which act contrariwise to one another at the outset andthen assist each other) to rotate in the anticlockwise and clockwisedirection, respectively, until reaching the end position as defined byfixed abutments 77-78 (FIG. 7). Subsequently, the driving shaft 76 isrotated so as to cause the displacement of the rod 74 towards theposition of FIG. 8, so that, due to the effect of the rotation of thesupporting members 70-71, the springs 64-65 urge the movable arms 55-56again towards a clockwise and an anticlockwise rotation, respectively,said rotation being prevented by two abutments 79-80 as carried by thesupports 70-71. Under the conditions of FIG.8, the switch is preset fora new closure operation (which can be effected by the reversedisplacement of the rod 74).

Still conformant with the features of this invention, there is theembodiment of FIGS. 9-11, in which the two couples of fixed and movablecontacts of the two releases of each pole of the switch are connected tothe two feeding and load terminals (not shown) by means of a currentpath formed by two closed loops (arrows B) which comprises a first rigidconductor 101, a first fixed arm 103, a first fixed contact 105, a firstmovable contact 107, a movable plate 109, a second movable contact 108,a second fixed contact 106, a second fixed arm 104 and a second rigidconductor 102. The movable plate 109, which is a supporting member forthe movable contacts 107-108, is held by a fixed sleeve 110 equippedwith two peripheral'notches 111-112, in whose interior two rollers113-114 can be engaged, which are carried by arms 115-116, the latterbeing rotatably'carried by a T-shaped rod 117 which is slidably housedwithin the sleeve 110 and is driven by a driving shaft 118 through alever 119. Two springs 120-121 are active upon the arms 115-116 so as tourge them against one another.

In operation, whenever a short circuit or anyhow a strong overcurrent isexperienced, the strong electrodynamic forces as produced by thecurrents of opposite signs which flow through the fixedarm 103 and themovable plate 109 (first closed loop) and the movable plate 109 and thefixed arm 104 (second closed loop) urge the plate 109 to overcome theholding bias imparted by the springs 120-121 (on account of theengagement between the rollers 1 13-114 and the notches 111-112) and tobe withdrawn from the fixed arms 103-104 until reaching the end positionas defined by an abutting relationship with fixed abutments 122-123. Thesubsequent displacement of the rod 117, which does not affect the plate109 and the sleeve 110, restores the engagement between the rollers113-114 and the notches 111-112 (FIG. 11) and thus presets the switchfor a new closure operation (which can be carried out by a reversedisplacement of the ,rod 117).

In another embodiment of the invention, as shown in FIGS. 12-14, the twocouples of fixed and movable contacts of the two releases of each poleof the switch, are connected, in turn, to the feeding and loadingterminals (not shown) by a current path having two closed loops (arrowsC) which comprises a first rigid conductor 151, a first flexible cable153, a first movable arm 155, a first movable contact 159, a movableconducting plate 161, a third movable contact 160, a fourth movablecontact 158, a second movable arm 156, a second flexible cable 154 and asecond rigid conductor 152. The two movable arms 155-156 are pivoted onfixed pivots 162-163 and, when in the closure position of FIG. 12, theyare maintained in such position by springs 164-165 inserted betweenfixed pivots 166-167 and pins 168-169 carried by the arms 155-156. Themovable plate 161, in turn, is rigidly connected to a slidable rod 170which is terminated by a wedge head 171 and is driven by a driving shaft172 through a lever 173.

In operation, whenever a short circuit or, anyhow, a strong overcurrentis experienced, the strong electrodynamic forces as produced by thecurrent of opposite signs which flow through the two closed loops formedby the movable arm 155 and the plate 161(first loop) and the movable arm156 (second loop) urge the movable arms to overcome the initial contrarybias of the springs 164-165 and to reach the end position as defined bythe abutting relationship with fixed abutments 174-175 (FIG. 13). Thepresetting of the switch for the subsequent closing operation can thenbe obtained by displacing the rod 170 so as to allow the wedge head 171of the latter to penetrate between the two confronting backs of the arms-156, so as to overcome the initially counteracting bias of the springs164-165 and to restore the arms 155-156 to the other end position asdefined by the abutting relationship with fixed abutments 176-177 (FIG.14). The closure of the switch can then obviously be carried out bydisplacing the rod in the opposite direction.

Lastly, FIGS. 15 to 17 show the case of a switch hav- I ing a singlerelease per pole, constructed in accordance with the principles of theinvention. The structure of this switch is practically equal to one halfof the structure of the switch as shown in FIG. 6 to 8. Thus, it willnot be described in detail herein and, to the ends of its understanding,reference will be had to the above mentioned FIGS. 6 to 8, of which thesame reference numerals have been used herein also. The only fact whichdeserves emphasis herein is that, in the present case, the two contacts57 and 59 are connected to the feed and load terminals 91-92 by acurrent path (arrows D) formed by a single closed loop, of which thesupporting members 55 and 61 are two parallel branches through whichcurrents with opposite signs flow.

It will obviously be understood that, just as it is possible toconstruct a switch having a single release per pole, which substantiallycorresponds to one half of the switch of FIG. 6 to 8, it will belikewise possible to construct switches having a single release per polewhich substantially correspond to one half of the switches shown in FIG.1 to 5, 9 to 11 and 12 to 14. These switches will be obviouslycharacterized by a current path forming a single closed loop, in whichthe supporting members are two parallel branches through which currentsof opposite signs flow.

What is claimed is:

1. A current-limiting electric switch having at least one release perpole, each release comprising two contacts carried by the respectivesupporting members, said contacts being electrically connected to afeeding terminal and to a loading terminal through a current path ofwhich, when the contacts are closed, said supporting members form twoparallel branches through which currents of opposite signs flow, so thata current increase beyond a predetermined limit produces in saidbranches electrodynamic repulsion forces such as to overcome thecontrary bias of resilient holding means and to cause the supportingmembers to be set apart for separating the contacts, characterized inthat said parallel branches form a portion of a closed loop formed bysaid current path in correspondance with each release.

2. A switch according to claim 1, equipped with two releases per pole,characterized in that said current path makes up two closed loops.

3.- A switch according to claim 2, characterized in that the tworeleases comprise first contacts placed at the ends of a commonconducting supporting member and respective second contacts placed atthe ends of respective movable arms the latter being located andelectrically connected to the feed and load terminals so that the twocurrent paths which electrically connect said terminals to said secondcontacts may form respective open loops which, as the contacts areclosed, are

closed and connected to one another by said common conducting supportingmenber.

4. A switch according to claim 3, characterized in that said secondcontacts are carried by rotatable arms and are maintained in the closedposition by resilient means which are urged, by the rotation of the armsfor effecting the rotation of the arms under the control of theelectrodynamic repulsion forces; to switch from a biassing condition toa condition of aid to said rotation.

5. A switch according to claim2, characterized in that the two releasescomprise respective fixed contacts placed at one end of respective fixedarms arranged and electrically connected to the feed and load terminalsso that the two current paths which electrically connect said terminalswith said fixed contacts from respective open loops, the two releasesfurther comprising respective movable contacts arranged at the ends of amovable common conducting supporting member for closing said loops.

6. A switch according to claim 5, characterized in that said commonmovable conducting supporting member is fastened to a translatablesupporting member which is held in the contact-closing position byresilient means of the groove and tongue type.

7. A switch according toclaim l, equipped with a single release perpole, characterized in that said current path is a single closed loop.

8. A switch according to claim 7, characterized in that the releasecomprises a movable contact carried by a rotatable arm which ismaintained in the closed position by resilient means which are urged, bythe rotation of the arm for the separation of the contacts under thecontrol of the electrodynamic repulsion forces, to switch from abiassing condition to a condition of aid to said rotation.

9. A switch according to claim 7, characterized in that the releasecomprises a movable contact carried by a translatable arm which ismaintained in the closed position of the contacts by resilient means ofthe groove and tongue type.

1. A current-limiting electric switch having at least one release perpole, each release comprising two contacts carried by the respectivesupporting members, said contacts being electrically connected to afeeding terminal and to a loading terminal through a current path ofwhich, when the contacts are closed, said supporting members form twoparallel branches through which currents of opposite signs flow, so thata current increase beyond a predetermined limit produces in saidbranches electrodynamic repulsion forces such as to overcome thecontrary bias of resilient holding means and to cause the supportingmembers to be set apart for separating the contacts, characterized inthat said parallel branches form a portion of a closed loop formed bysaid current path in correspondance with each release.
 2. A switchaccording to claim 1, equipped with two releases per pole, characterizedin that said current path makes up two closed loops.
 3. A switchaccording to claim 2, characterized in that the two releases comprisefirst contacts placed at the ends of a common conducting supportingmember and respective second contacts placed at the ends of respectivemovable arms the latter being located and electrically connected to thefeed and load terminals so that the two current paths which electricallyconnect said terminals to said second contacts may form respective openloops which, as the contacts are closed, are closed and connected to oneanother by said common conducting supporting menber.
 4. A switchaccording to claim 3, characterized in that said second contacts arecarried by rotatable arms and are maintained in the closed position byresilient means which are urged, by the rotation of the arms foreffecting the rotation of the arms under the control of theelectrodynamic repulsion forces; to switch from a biassing condition toa condition of aid to said rotation.
 5. A switch according to claim 2,characterized in that the two releases comprise respective fixedcontacts placed at one end of respective fixed arms arranged andelectrically connected to the feed and load terminals so that the twocurrent paths which electrically connect said terminals with said fixedcontacts from respective open loops, the two releases further comprisingrespective movable contacts arranged at the ends of a movable commonconducting supporting member for closing said loops.
 6. A switchaccording to claim 5, characterized in that said common movableconducting supporting member is fastened to a translatable supportingmember which is held in the contact-closing position by resilient meansof the groove and tongue type.
 7. A switch according to claim 1,equipped with a single release per pole, characterized in that saidcurrent path is a single closed loop.
 8. A switch according to claim 7,characterized in that the release comprises a movable contact carried bya rotatable arm which iS maintained in the closed position by resilientmeans which are urged, by the rotation of the arm for the separation ofthe contacts under the control of the electrodynamic repulsion forces,to switch from a biassing condition to a condition of aid to saidrotation.
 9. A switch according to claim 7, characterized in that therelease comprises a movable contact carried by a translatable arm whichis maintained in the closed position of the contacts by resilient meansof the groove and tongue type.